FIELD OF THE INVENTION
The present invention relates to a novel mixture for stabilizing polyurethanes, containing (a) an amine based on a derivative of 1,2,2,6,6-tetramethylpiperidine, (b) a mixture of substituted 2-phenylbenzotriazoles and (c) .alpha.-tocopherol, if necessary mixed with tris-(nonylphenyl) phosphite, and polyurethanes which contain the novel stabilizer mixture.
It is known that polyurethanes are very rapidly destroyed by the effect of light. This descruction usually appears in the form of yellowing or discoloration and in embrittlement of the polymeric material.
A number of light stabilizers for polyurethanes have already been described, the stabilizers belonging to the class consisting of the sterically hindered amines, the class consisting of the UV absorbers and the class consisting of the deoxidants. However, it has to date been impossible to achieve any satisfactory protection from destruction by the effect of light by using the known stabilizers in polyurethanes.
Although improved light stabilization is achieved by using combinations of the compounds of the stated classes, the high concentration of additives which is required for effective protection often leads to undesirable changes in the polymer properties and to compatibility problems, for example exudation, chalking, formation of coatings or color changes.
Stabilizers which are in the solid state also frequently have the disadvantage that they are poorly soluble, or dissolve only slowly, in the starting components of the polyurethane, which may lead to processing problems, such as blocking of nozzles or longer processing times.